1. Field of the Invention
This invention relates generally to video data transmission systems and specifically to a video-on-demand system controlled by viewers in real-time. More particularly, it relates to the interactive delivery of digital video data on demand from a video library which is referenced by a digital video data server for real-time distribution to multiple display systems controlled by viewers.
2. Background Information
Distribution of full motion video data has evolved from the earliest days of television broadcasting to meet viewer demand and respond to technological change. The original method of video data distribution in early television demonstrations used point-to-point wiring between a camera and a video monitor. This method employed a single program controlled entirely by the person operating the camera. This was followed shortly thereafter by broadcast stations transmitting fixed schedules of programming to the public via Ultra-High Frequency (UHF) and Very-High Frequency (VHF) television channels. The number of broadcast channels was limited, however, both by government regulation and the physics of over-the-air broadcast technology. In time, an emerging cable television industry distributed a greater number of programs on many more channels over dedicated land lines or microwave satellites to viewers. The number of possible programs to view went up, but control over the content and timing of the programming was in the hands of the cable television companies, not the viewers. In the last fifteen years, the widespread use of video cassette recorders (VCRs) has changed the viewing habits and control capabilities of viewers. With a VCR, a viewer has complete control over the content and timing of what he/she is viewing. However, using a VCR to control program viewing has some inherent problems. The viewer must either record a broadcast program for later viewing or venture out to the video store to select and obtain the desired program's cassette. The later requires a second trip to the video store to return the cassette after viewing the program. Viewer selection may be frustrated if the desired program is unavailable because all copies of the program are already rented, the program is not in the store's stock, or the store is closed.
In order to solve some of the problems associated with the cable and video cassette rental technologies, various video-on-demand (VOD) or programming-on-demand systems have been proposed to provide viewers with the timing and content control of a VCR coupled with the convenience of a cable system. In Walter, U.S. Pat. No. 4,506,387, a programming-on-demand cable system is disclosed which allows a viewer to select a program to view from a library of programs. The selected program is transmitted at a high, non-real-time rate over a dedicated fiber optic line to a receiving station at the viewer's location. This system allows a viewer to select a start time for a selected program at any time after the selected program has been received, but does not provide the capability for other VCR-type controls such as pause, rewind, fast-forward, or stop. The transmission station must be equipped to transmit the selected program to the viewer's site in non-real-time.
In Monslow, et. al., U.S. Pat. No. 4,995,078, a television broadcast system is disclosed that allows a viewer to select a program to watch at a prescribed time. This system is limited in that it requires multiple viewers in multiple locations to view the program at the time it is broadcast, rather than allowing each viewer to independently choose his/her own viewing time. The Monslow system is limited because it is based on cable television technology using land lines and there are a limited number of channels to broadcast programming on, thereby severely limiting the number of different programs to be simultaneously watched by many viewers (i.e., the number of viewers who can watch a program solely of their own choice is bound by the number of available channels in the system). This system also does not provide VCR-type controls over the broadcast to the viewer.
Lambert, U.S. Pat. No. 4,381,522, discloses a selective viewing system whereby a viewer can control the content of a broadcast channel by telephoning a cable television company. The selected program is scheduled and broadcast at a scheduled time. The viewer monitors a directory channel to determine when the requested program is to be broadcast over the cable channel, and then watches the program at the scheduled time rather than at a viewer selected time. This system is also limited by the number of cable channels and does not provide VCR-type control to the viewer.
The above described systems only communicated analog video signals. McCalley, et. al., U.S. Pat. No. 4,829,372, discloses an interactive communication system for transmitting digital video data to viewers. However, this system is designed to transmit still frame television data over a cable network and does not provide VCR-type control over full motion video. Pocock, et. al., U.S. Pat. No. 5,014,125, also discloses an interactive television system for transmission of still frame images over a cable network. A telephone network is used to communicate viewer requests and video data between the viewer's site and a central location. Both the McCalley. et. al., and Pocock, et. al., systems are limited in that they do not support full motion video-on-demand.
Telephone lines have been proposed as an alternate means of video data distribution to alleviate the problems associated with a limited number of cable channels. Litteral, et. al., U.S. Pat. No. 5,247,347, describes a public switched telephone network used as a distribution network for digital video signals in a video-on-demand system. The distribution network is described in detail, but little disclosure is made of a mechanism for efficiently providing digital video data to the viewer via the network. In addition, the Litteral, et. al., system is limited because it is designed to work only with ISDN packets and existing telephone lines controlled by the telephone company central office switching equipment.
A complete digital video data transmission system is disclosed in Yurt, et. al., U.S. Pat. No. 5,253,275. The Yurt, et. al., system sends compressed digital video data on demand to viewers over standard telephone lines, cable lines, or satellite broadcast channels in less than real-time, for later playback or recording. The data is then decompressed for display on a television monitor. This system appears to solve some of the problems and limitations of systems described above, but it is limited in the numbers of viewers it can service by the bandwidth of its control computer. It does not address the problems relating to overall system throughput when providing service to more than a small number of viewers.
Another digital video data file server system is described in Mincer, et. al., U.S. Pat. No. 5,262,875. This system provides digital video data distribution, but, like Yurt, et. al., it does not address problems of system throughput when more than a trivial number of viewers are to be supported. The Mincer, et. al., system provides a file server for retrieving compressed, digital video data from a library of programs, and a plurality of playback units for decompressing and transmitting the video data to viewers. This system is designed to accept video data in less than real-time for storage in its library of programs, and subsequently transmit the data on demand in real-time to a viewer's playback station. The use of video data compression increases the amount of video data transmitted per unit time. The Mincer, et. al. system is deficient because the number of viewers it can service is bound by the transfer rate of the magnetic disk drive used to store the video data. The number of viewers simultaneously supported by this system appears to be as small as ten.
As described above, prior art systems do exist that provide a viewer VCR-type control over the delivery of digital video data. However, these systems are deficient in that they are severely limited in the number of viewers they can support. Retrieving many requests for full motion, digital video data from a mass storage device and forwarding the data to a distribution network for transmission to many viewers requires vast resources in terms of I/O access times, channel speeds, and overall system throughput. The bottleneck in successfully providing service to many viewers is not in the distribution network, but in the file server used to selectively access the digital video data, whether compressed or not. Accordingly, new techniques and system architectures are needed to effectively provide digital video-on-demand concurrently to many viewers.